ISS Managers Mull Spacewalks To Address Power, Cooling

HOUSTON — With Space Exploration Technologies\x92 Dragon supply ship reaching the International Space Station (ISS), NASA plans to step up the troubleshooting of elusive ISS electrical and coolant system issues that will likely lead to a pair of U.S. spacewalks, possibly within the next several weeks.

The first issue is associated with a significant short on Sept. 1 that prompted a shutdown of the 3A solar power channel, one of eight channels that provide electricity to the station; the second is a longer-running ammonia leak in the P-6 solar power truss, which may rise in urgency.

The coolant leak, which began to increase in June, could trip coolant system limits by early January, Mike Suffredini, NASA’s ISS program manager, told an Oct. 6 news briefing at Kennedy Space Center during the SpaceX Dragon launch countdown.

Station commander Sunita Williams and Japanese astronaut Akihiko Hoshide expect to grapple and berth Dragon using the orbiting lab’s Canadian robot arm early Oct. 10, a little more than 60 hr. after a successful launch from Cape Canaveral.

“We need to consider whether we need to do a [spacewalk] sooner rather than later, and if we decide we need to do it sooner, we will need to do it with Suni and Aki,” Suffredini says.

Williams and Hoshide, who teamed to replace the failing external Main Bus Switching Unit-1 during spacewalks on Sept. 5 and Aug. 30, are scheduled to return to Earth on Nov. 12 aboard a Russia Soyuz spacecraft with cosmonaut Yuri Malenchenko, ending a four-month mission. Replacements Tom Marshburn of NASA and Chris Hadfield of the Canadian Space Agency, who have been trained for U.S. segment spacewalks, are currently scheduled to launch on a Soyuz capsule with cosmonaut Roman Romanenko on Dec. 19.

“If the data tells us we can go much beyond January, that would give us the option to just wait. We will talk about that thoroughly in the near future,” said Suffredini. “I think you will see us lean toward trying to get [spacewalks] done before Suni and Aki leave,” Suffredini says.

As the station’s U.S. segment assembly drew to a close in mid-2011, NASA attempted to curtail time-consuming spacewalk activities to focus the astronauts’ efforts on science experiments and technology demonstrations.

The P-6 truss and twin solar array were launched in late 2000 (STS-97, December 2000) to provide the initial electricity to the station’s growing U.S. segment. It was moved to its permanent port-side outboard location in late 2007 (STS-120, October-November 2007).

Potential sources of the leak include the coolant pump, radiator or the plumbing associated with the 12-year-old truss.

As far as the short, station engineers are looking at several possible culprits, including a direct current switching unit, a voltage regulating sequential shunt unit or the beta gimbal assembly that adjusts the angle of the solar panels to the Sun.